The present invention relates to a semiconductor device having a circuit constituted of a thin film transistor (hereinafter, referred to as TFT) and manufacturing method thereof. More particularly, the invention relates, for example, to an electrooptical device exemplified by a liquid crystal display panel and a light-emitting device exemplified by an electroluminescence display device and electronic apparatus on which electrooptical devices as described-above are mounted as component parts thereof.
In this specification, the term “semiconductor device” means every device that functions by using the semiconductor characteristics; i.e., electrooptical devices, light-emitting devices, semiconductor circuits and electronic apparatuses are all included in the semiconductor device.
Recently, a technique, in which a thin film transistor (TFT) is constituted using a semiconductor thin film (approximately several nm-several hundreds nm in thickness) having an insulated surface on a substrate, has attracted attention. The thin film transistor has been widely applied to electronic devices such as IC, electrooptical device and so on; in particular, it is desired to develop the same as a switching element for display device on various apparatuses.
Particularly, an active matrix type liquid crystal display device, which is provided with switching element of TFT to each display pixel disposed on a matrix, has been developed.
As for the active matrix type liquid crystal display device, a development to extend the effective screen area in the pixel section is now under progression. To enlarge the area of the effective screen area, it is necessary to reduce the area occupied by the TFT disposed in the pixel section as small as possible. Further, in order to reduce the manufacturing cost, a development to build a drive circuit on the same substrate along with the pixel section is also under progression. When the drive circuit and the pixel section are formed on the same substrate, compared to the case that the drive circuit is mounted in a manner of TAB, there is a tendency that the area occupied by area other than the pixel area, which is called as frame rim area, become large. It is also requested that, in order to reduce the frame rim area, the size of the circuit constituting the drive circuit should be formed further smaller in size.
Particularly, in an organic light emitting device (OLED), a plurality of TFTs, which are different from each other in function, for one pixel. Further, in the liquid crystal display device also, an attempt to form switching TFT and memory element such as SRAM or the like in a pixel has been made. Furthermore, when the pixel section and the drive circuit are formed on the same substrate, it is requested to miniaturize the same as small as possible. As described above, when a plurality of elements are formed within a limited area, a design, in which the elements are disposed on a plane, or a design, in which the elements are piled up, are conceivable. In the case that the elements are disposed on a plane, since the required area allowed to occupy is limited, when the area is limited, a limitation resides therein. Also, in a design that the elements are piled up, for example, when two TFTs are piled up, the number of steps is increased simply by two times or more resulting in a complication in the steps, an increase of cost, a reduction of the throughput and a reduction of the yield.
As for designs of conventional techniques in which elements are piled up; for example, Japanese Unexamined Patent Application Publication No. 10-93099 and Japanese Unexamined Patent Application Publication No. 10-93100 respectively disclose a structure in which an FET and a TFT are piled up on a semiconductor substrate. Also, in Japanese Unexamined Patent Application Publication No. 11-40772, a structure, in which TFTs are disposed being piled up and interposed by insulating film on a bulk transistor, is disclosed. According to these Publications, in any case, an FET or a bulk transistor is formed using a semiconductor substrate, and a TFT is simply formed thereon.
An object of the invention is, in order to promote the tendency toward the foreseeable further compaction in each display pixel pitch accompanying the tendency of higher precision (increase in pixel number) and miniaturization in electrooptical device exemplified by liquid crystal display device, light-emitting device having OLED and semiconductor device, to form a plurality of elements within a limited area and to integrate the same by compacting the area occupied by the elements.